Induction furnace



Sept. 22, 1931. P. H. BRACE INDUCTION FURNACE Filed Jan. 23, 1930 Fly.

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INVENTOR Porter H. Brace Patented Sept. 22, 1931 UNITED STATES PATENT OFFICE A PORTER E. BRACE, 0] FOREST HILLS, WILKINBBUBG, PENNSYLVANIA, ASSIGNOB TO WESTINGHOUSE I PENNSYLVANIA ELECTRIC & KANUI'ACTUBING COMPANY, A CORPORATION OI INDUGIION FURNACE Application fled January as, mo. m in. 422,770.

electrical condition of electric-insulating material in an induction furnace.

Another object of my invention is to provide a guard wall located around a crucible of an induction furnace that shall cooperate 15 with the crucible to prevent molten metal which may escape therefrom, from coming into contact with the inductor coil.

Another object of my invention is to provide electrical means operatively and con- 20 tinuously associated with the furnace structure for indicating the electric insulating material and the mechanical condition of the crucible.

Another object of my invention is to provide a ground shield operatively associated with, and incorporated in, the furnace structure for preventing accidental shock to an operator working around the furnace.

In practicing my invention, I provide a suitable furnace structure of the surroundedpool type having a suitable outside casing, an inductor coil therein, substantially solid electric insulating material immediately within the coil, a laminated or sub-divided ground shield within the coil, and a guard wall spaced from, and on the outside of, a crucible or lining for containing the material to be melted in the furnace. The ground shield may be water-cooled and is supported by, and in, granular electric-insulating material which fills the space between the outer casing and the guard wall. v

I provide also one or more indicating instruments, a source of electric energy and connections between the indicating instruments, the source of energy and certain elements of the furnace structure to indicate the electrical and/or mechanical condition 5 of certain elements of the furnace.

In the single sheet of drawings,

Figure 1 is aview, in vertical lateral section, of an induction furnace embodyin my invention, an indicating system associated therewith being shown schematically,

Fig. 2 is a view, in side elevation, of one form of water-cooled ground shield,

Fig. 3 is a top plan view of the element shown in Fig. 2,

Fig. 4 is a developed view of a modified form of water-cooled ground shield, and,

Fig. 5 is an end view thereof.

An induction furnace 11 includes an outer casing 12 which is here shown as made of a suitable metal and which may be provided with any suitable or desirable means to permit of tilting of the furnace to pour the metal or alloy which may be melted in the furnace, and I have not thought itnecessary to illustrate or describe such tilting arrangement or structure in detail, as it forms no part of my present invention.

An energizing coil 13 is located within, and radially spaced from, the casing 12 and. includes a plurality of turns of asuitable electrio-conducting wire or bar which is shown as being substantially rectangular in section. I- do not desire, however, to be limited to this articular shape of current-conducting mem er, as any suitable conductor may be 80 utilized.

A ground shield 14 is located within, and spaced from, the inductor coil 13 and, as it is necessary that this protecting shield be subdivided or laminated, and as I may desire to use a water-cooled shield, I have illustrated element or member14 more in detail in Figs. 2 and 3 of the drawings. An upper metallic conduit 16 of substantially open annular shape is provided, as is also a similar lower metal conduit 17 also of open annular shape. A plurality of relatively smaller metalhc pipes or conduits 18 extend between the two larger conduits 16 and 17 and are secured thereto in a fluid-tight manner. All of these conduits may be made of a metal or an alloywhich will be corrosion resistant, as well-as being able to withstand relatively high temperatures, and I may employ, for this purpose, one of the numerous alloys which have been developed for this, or similar urposes, such as some alloy of nlckel and stee Terminal conduits 19 may be provided for the top and bottom conduits 16 and 17, and electric-insulating flexible pieces of hose 21 may be provided on the respective ends 19 in order that there may be no electrical circuit available to include the water-cooled protecting shield.

A guard wall 22 of refractory material is located within the protecting shield 14 and is of substantially tubular shape having a bottom wall portion 23 which is provided with an outlet opening 24 therethrough. A crucible 26 is located within the guard wall 22. and may consist of a single unitary member, if the crucible is relatively small, or it may consist of a plurality of suitably shaped bricks or blocks of a refractory material, as is shown in Fig. 1 of the drawings. Each of the bricks or blocks, or at least a predetermined number thereof, may be provided with outer projections 27' in order that there may be a substantially annular space 28 between the guard wall 22 and the crucible 26. It is to be understood that the area of cross section of the lugs or projections 27 is relatively small and that the annular space 28 is substantially free and unobstructed and that the upper part or portion of the annular space 28 has free and unobstructed communication with the outlet opening 24 in the guard wall 22.

A relatively solid wall 31 of electric-in sulating material, which may be of mica, is located immediately within, and preferably in operative engagement with, the inner peripheral surface of the conductor constituting the coil 13. All of the space between the outside of the guard wall 22 and the inside of the tank or casing 12 may be filled with a ranular electric-insulating material 32 such, for example, as zirconium silicate which is, in general, a free-flowing sand and may be tamped or compac'.ed in place during the assembly of the furnace structure, including the elements hereinbefore described.

A cover for the furnace structure includes a metal member 33 of suitable shape and may also be provided with suitable lifting means (not shown) in order to permit of the removal of the cover structure to permit of filling the crucible with the raw material to be melted. A plurality of suitably shaped bricks or blocks 34 of a highly refractory high-temperature-resisting material is located within the cover member 33 and may be held therein by any suitable or desired means, among which may be included the use of properly shaped bricks or blocks, such as are shown in Fig. 1 of the drawings.

I have illustrated a modified form of water-cooled shield for the grounded protecting wall in Figs. 4 and 5 of the drawings.

A bottom conduit 36, as well as an upper conduit 37 of relatively larger size, is provided between which upwardly extend a plurality of small conduits 38, each of U-shape and properly connected, at their ends, to the conduits 36 and 37 Flexible hose members 41 and 42 are provided at the opposite ends of the conduits 36 and 37, by which connection may be made to a supply of cooling fluid, in a manner well known in the art.

Means for continuously indicating the electrical condition of the furnace structure includes two indicating instruments 44 and 46 which may be of any suitable electromagnetic type and are here shown as including a movable pointer 47, a core-member 48 and an actuating coil 49. Means for energizing the actuating coils 49 may include a battery 51, although I do not wish to be restricted to the use of a direct-current source of energy.

A plurality of conductors 52, 53 and 54 are provided, one end of conductor 52 beingconnected to the topmost turn of inductor coil 13, one end of conduc or 53 being connected to the protecting shield 14, and one end of conductor 54 being connected to the crucible 26 or to an electrode making contact with the charge. The other ends of these conductors are electrically connected to one set of terminals of a three-pole, manually 'operable switch 56. The other terminals of switch 56 are connected, by suitable electric circuit conductors, to one of the terminals of coils 49, the other terminals of which are connected together and, through another conductor 59, to one terminal of the source 51.

A ground 61 is provided which is connected to conductor 53 and, therefore, to the protecting shield 14.

I have found that there is a large difference in the operating characteristics of an induction furnace, and, more particularly, in the operation of the granular insulating material 32 and the crucible 26 when using a furnace of this type for the melting of ferrous alloys and when using it for melting non-ferrous alloys.

I have found that some of the metals and non-ferrous alloys are vaporized and that these, or vaporized metal oxides, if they escape through the wall of the crucible, will diffuse into the sand and will cake it into a rigid or solid mass which may develop fissures because of temperature changes. This process is a gradual one and I have found that it'is very hard to prevent the formation of small cracks in the crucible, even though it be a unitary crucible, with the possibility of the escape of molten metal through these minute fissures and the infiltration of this escaped molten metal into the sand, which process ma continue until it is detected by reason of t e sudden escape of a large volume of molten metal or by reason of some accident to an attendant.

In order to take care of this condition, which I have found it almost impossible to avoid, even with the greatest of care in the manufacture of the crucible and the assembly of the furnace structure, I provide, first of all, the guard wall 22 which is made of a refractory material and is spaced a small distance from the outside of the crucible. case of small fissures appearing in the crucible through which molten metal may escape, it is evident that the annular space 28 permits of conducting away the molten material along the outside of the crucible and outwardly and downwardly through the opening 24, from which it may be conducted into a suitable emergenc crucible or ladle. In other words, instead 0 rmittin molten metal that escapes 'throug the wall of the crucible from leaking into or entering the granular material 32, I conduit it away and its appearance at the bottom of the furnace structure is an indication of relatively -dan gerous conditions in the furnace structure calling for immediate consideration and proper repairs of the damaged element.

It is of course, possible that a uard wall 22 may itself fail if retained in t e furnace structure while the crucible itself has been replaced and rebuilta number of times. Should the metal escaping through the crucible 26 flow through the guard wall 22 at some point, it will come into operative engagement with the shield 14 and thereby establish a substantially direct electrical connection between the crucible or the charge therein and the shield 14, and in this case, a suitable indication will be given by instrument 46, thus calling attention to the damaged condition of that part of the furnace structure between the molten metal in the crucible and the shield 14.

While I have indicated a visual signal, I may provide contact terminals in each of the indicating instruments which may be connected to an audible signal so that a visual signal only will be given in the case of relatively small decreases in the value of the insulation resistance between the crucible or the metal therein and the shield, while an audible signal will be given in case of a complete break down of the insulation resistance between these same members.

The same comments will hold, if for an reason, the metal or alloy escaping throug the crucible and the guard wall should happen to avoid contact with the shield 14 by reason of the spaces between the individual vertically extending elements thereof and should reach the individual turns of inductor coil 13, as by damaging the insulatin wall 31. In this case, instrument 44 woul indicate the electrical condition of the electric insulating material. An operator can,

therefore, easily determine where the insulation has broken down, that is, whether the electric insulation between the crucible and the round shield has broken down or whether t e electric insulation between the ground shield and the coil has been damaged or destroyed.

It is, of course, desirable to maintain the temperature of the inductor coil and of the outer casing at a relativel low value and it is for this reason that may make the shield 14 water or fluid cooled, a provision which may be necessary in very large furnaces.

I have illustrated the electrical conductors 52, 53 and 54 as being connected at the upper part of the respective members to which they are connected and, while this is not absolutely necessary, I prefer to do so, as any contact with the furnace elements will be effected more probably at the top of the furnace structure than at the inside or at the bottom thereof.

The furnace structure embodying my invention thus rovides not onl a guard wall which imm iately surroun s the crucible but is spaced therefrom, in order that molten material in the crucible which escapes through the walls thereof may be conducted away from the coil and the insulation and, by its appearance at the bottom of the furnace structure, give an indication of the fact that a leakage exists, but it also provides electrical means for continuously indicating the electrical condition of the furnace structure, and

more particularly, of the value of the electrical resistance of certain of its parts. It is, of course, obvious that records may be kept of the readings of the indicating instruments at the beginning of the operation of the furnace, more particularly after it has been thoroughly dried out, in order that later readings may be compared therewith, comparative readings giving an indication of the deterioration, if any, of certain parts of the furnace structure.

I desire it to be understood also that, while I have used only the term cruciblel, I do not desire to be limited to a removable crucible or to that form shown in the drawings, but desire to include thereunder any lining provided in a furnace chamber in which materials may be melted.

Various modifications may be made in the device embodying my invention without departing from the spirit andscope thereof and I desire, therefore, that only such limitations shall be placed thereon as are imposed by the prior art and set forth in the appended c aims.

I claim as my invention:

1. An induction furnace includin a crucible, an induction coil therearoun and a grounded water-cooled protecting shield between the crucible and the induction coil.

' 2. An induction furnace including a crucible, an induction coil therearound, a guard Wall adjacent to and supporting said crucible, and means between the guard wall and the 5 crucible for providing a drainage-passa e for molten metal esca ing from said crucible.

3. In an inductlon furnace having a crucible and an induction coil extending therearound, a ground shield located between the coil and the crucible, electric insulating material between the crucible, shield and coil, and electric means operatively associated with the crucible, shield and coil to indicate the electrical condition of the electric-insulating material.

4. In an induction furnace having a crucible and an induction coil located therearound, and electric-insulating means located between the induction coil and the crucible, electric 2 means operatively associated with the coil and the crucible to indicate the electrical condition of the electric-insulatin means.

5. In an induction furnace aving a crucible, an induction coil located therearound and electric-insulating material between the coil and the crucible, an indicating instrument, a source of electric energy and electric connections between the instrument, the source of energy, the coil and the crucible to indicate the electrical condition of the electric-insulating material.

4 6. In an induction furnace having-a crucible and an induction coil therearound, a guard wall surrounding the crucible, a grounded shield between the guard wall and the coil, electric-insulating material between the guard wall and the grounded shield, and means for indicating the electrical condition of the electric-insulating material and of the guard wall including an indicating instrument, a source of electric ener and connections between the indicating instrument, the source of electric energy, the crucible and the grounded shield.

7. In. an induction furnace having a crucible, an induction coil therearound and granular electric-insulating material therebetween, a guard wall of solid refractory material located between the insulation and the crucible to prevent molten metal escaping through the crucible from engaging the granular electric-insulating material.

8. In an induction furnace having a crucible, an induction coil therearound and granular electric-insulating material thereetween, a guard wall of solid refractory material located between the insulation and the crucible and spaced from the crucible to prevent molten metal escaping through the crucible wall from engaging the granular electric-insulating material, said guard wall having means to permit said escaping molten metal to flow away from the assembled furnace structure.

9. In an induction furnace having a crucible, an induction coil therearound and electric-insulating material between the coil and the crucible, an electric-conducting shield in said electric-insulating material, and electric ary, 1930.

PORTER H. BRACE. 

